Polishing system

ABSTRACT

A polishing system includes a wafer support that holds a wafer, the wafer having a first diameter. The polishing system further includes a first polishing pad that polishes a first region of the wafer, the first polishing pad having a second diameter greater than the first diameter. The polishing system further includes an auxiliary polishing system comprising at least one second polishing pad that polishes a second region of the wafer, wherein the second polishing pad has a third diameter less than the first diameter, and the wafer support is configured to support the wafer during use of the first polishing pad and the auxiliary polishing system.

PRIORITY CLAIM

The present application is a divisional of U.S. application Ser. No.13/706,506, filed Dec. 6, 2012, which is incorporated herein byreference in its entirety.

BACKGROUND

Integrated circuits are typically fabricated on a semiconductor wafer,with many individual dies manufactured simultaneously on the same wafer.Processing steps are used to form layers of metal and dielectrics on thesemiconductor wafer to define interconnect structures, as well as activeand passive electronic devices. Many of the processing steps result innon-planar layers. However, it is often desirable for layers of theintegrated circuit to have uniform thickness. Thus, polishing isrequired both to provide uniform thickness, and a smooth layer surface,which not only ensure device performance, but also aid subsequentprocessing steps.

Polishing techniques include mechanical planarization (MP) and chemicalmechanical planarization/polishing (CMP). A typical CMP system willinclude a large polishing pad, on which a chemical slurry is introducedto facilitate wafer polishing, and a polishing head. To polish asemiconductor wafer, the semiconductor wafer is held by the polishinghead, and the polishing head simultaneously applies a force to press thesemiconductor wafer against the rotating polishing pad, while alsorotating the semiconductor wafer.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present embodiments, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a diagram of a polishing system in accordance with variousembodiments of the present disclosure;

FIG. 2 is a top view of a polishing pad capable of translation androtation in accordance with various embodiments of the presentdisclosure;

FIGS. 3A and 3B are top views of multiple polishing pads used in thepolishing system in accordance with various embodiments of the presentdisclosure;

FIG. 4 is a top view of a polishing pad including a cleaning sub-systemin accordance with various embodiments of the present disclosure;

FIG. 5 is a flowchart of a polishing process in accordance with variousembodiments of the present disclosure;

FIG. 6 is a diagram of a polishing system in accordance with variousembodiments of the present disclosure;

FIG. 7 is a diagram of a polishing head of the polishing system inaccordance with various embodiments of the present disclosure;

FIGS. 8 to 13 are illustrations of wafer contours following completionof a first polishing process in accordance with various embodiments ofthe present disclosure;

FIG. 14 is a detailed view of an auxiliary polishing system of FIG. 1 inaccordance with various embodiments of the present disclosure;

FIG. 15 is a flowchart of a full polishing process in accordance withvarious embodiments of the present disclosure;

FIG. 16 is a flowchart of a second polishing process in accordance withvarious embodiments of the present disclosure; and

FIGS. 17 to 20 are diagrams of an auxiliary bevel polishing unitperforming bevel polishing in accordance with various embodiments of thepresent disclosure.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the present embodiments are discussed in detailbelow. It should be appreciated, however, that the present disclosureprovides many applicable inventive concepts that can be embodied in awide variety of specific contexts. The specific embodiments discussedare merely illustrative of specific ways to make and use the disclosedsubject matter, and do not limit the scope of the different embodiments.

Embodiments will be described with respect to a specific context, namelya polishing system and the like. Other embodiments may also be applied,however, to other polishing systems which are used to polish materialsurfaces.

Throughout the various figures and discussion, like reference numbersrefer to like components. Also, although singular components may bedepicted throughout some of the figures, this is for simplicity ofillustration and ease of discussion. A person having ordinary skill inthe art will readily appreciate that such discussion and depiction canbe and usually is applicable for many components within a structure.

Polishing heads hold onto a circular semiconductor wafer by use of aretaining ring, and press the semiconductor wafer against a spinningpolishing pad to planarize and/or polish a face of the semiconductorwafer. As the semiconductor wafer spins, due to the nature of angularmotion, tangential velocity increases from the center of thesemiconductor wafer to its edge. Thus, if the semiconductor wafer werepressed against the polishing pad by uniform pressure, edges of thesemiconductor wafer would be polished more heavily than central regions.To address this issue, applicators are introduced in the polishing headto vary curvature of the semiconductor wafer during polishing, whichcompensates for the differences in tangential velocity over the radiusof the semiconductor wafer. The applicators, which may includemechanical parts, such as springs or pistons, press against thesemiconductor wafer to cause temporary curvature thereof. For variousreasons, including aging, defects, and damage, the applicators do notperform as expected. As a result, the semiconductor wafer may exhibituneven polishing after the polishing process is completed, which affectsyield and throughput.

In the following disclosure, a novel polishing system is introduced,which uses a polishing pad having diameter smaller than thesemiconductor wafer to achieve high uniformity when polishing thesemiconductor wafer. In the polishing system disclosed herein, thesemiconductor wafer may lie face-up on a table, while the polishing padpolishes the semiconductor wafer using a combination of a proper slurryand downward pressure. The polishing pad, being smaller than thesemiconductor wafer, may sweep over the surface of the semiconductorwafer in a pattern that is programmable, or even adaptable based onin-line metrology data. Multiple polishing pads may be usedsequentially, simultaneously, or in a combination of the two to increaseflexibility and throughput.

The polishing system also provides a cleaning operation that can beperformed without removing the semiconductor wafer to a separatecleaning station. After any polishing operation, a cleaning operationmay be performed to remove excess slurry, for example. In the polishingsystem disclosed herein, the cleaning operation may be performed by aroller brush in combination with distilled water or a cleaning agent,for example. With the semiconductor wafer still face-up on the table,the roller brush is lowered onto the semiconductor wafer to clean thesemiconductor wafer. Following the cleaning operation, further polishingoperations may be performed using the polishing pad disclosed hereinwithout removing the semiconductor wafer from the table.

The polishing pad in some embodiments also acts as an auxiliarypolishing pad(s) in a rework operation to polish the semiconductor waferin certain regions, while leaving other regions of the semiconductorwafer unaffected. The polishing pad is smaller than the semiconductorwafer, and is controllable in three dimensions. Taking metrology datafollowing a first polishing process on a main polishing pad having adiameter greater than that of the semiconductor wafer, a secondpolishing profile can be programmed into the polishing system, and theauxiliary polishing pad can be used in conjunction with a polishing headto rework the semiconductor wafer under process, without taking thesemiconductor wafer offline from the polishing system. Multiple smallauxiliary polishing pads can be used in conjunction with the polishinghead to provide even greater polishing profile flexibility andthroughput. In some embodiments, a bevel polishing pad is also used inconjunction with the polishing head to polish a bevel region of thesemiconductor wafer.

FIG. 1 is a diagram of a polishing system 10 in accordance with variousembodiments of the present disclosure. A wafer table 120 supports andoptionally rotates a semiconductor wafer 200 (or simply “wafer 200”) tobe polished. A polishing pad 111 of a polishing head 110 polishes afront face 201 of the semiconductor wafer 200. Width w2 (e.g., outerdiameter) of the polishing pad 111 is shorter than width w1 (e.g., outerdiameter) of the semiconductor wafer 200. In some embodiments, arotation control mechanism 121 controls rotation of the wafer 200, and aslurry delivery mechanism 122 mixes, stores and/or delivers chemicalslurry to the front face 201 of the wafer 200 to enable chemicalmechanical polishing (CMP). Metrology tools 130 read parameters of thewafer 200 before, during, and/or after polishing of the wafer 200 by thepolishing system 10. A system controller 140 controls variables of thepolishing process performed by the polishing system 10.

In some embodiments, the semiconductor wafer 200 includes an elementarysemiconductor including silicon or germanium in crystal,polycrystalline, or an amorphous structure; a compound semiconductorincluding silicon carbide, gallium arsenic, gallium phosphide, indiumphosphide, indium arsenide, and indium antimonide; an alloysemiconductor including SiGe, GaAsP, AlInAs, AlGaAs, GaInAs, GaInP, andGaInAsP; any other suitable material; or combinations thereof. In someembodiments, the alloy semiconductor has a gradient SiGe feature inwhich the Si and Ge composition change from one ratio at one location toanother ratio at another location of the gradient SiGe feature. In someembodiments, the gradient SiGe feature is formed over a siliconsubstrate. In some embodiments, the gradient SiGe feature is strained.Furthermore, in some embodiments, the semiconductor wafer 200 is asemiconductor on insulator, such as a silicon on insulator (SOI), or athin film transistor (TFT). In some examples, the semiconductor wafer200 includes a doped epitaxial layer or a buried layer. In otherexamples, the compound semiconductor wafer 200 has a multilayerstructure, or the wafer 200 may include a multilayer compoundsemiconductor structure. In some embodiments, the semiconductor wafer200 includes an epitaxial layer. For example, the wafer 200 has anepitaxial layer overlying a bulk semiconductor. Furthermore, in someembodiments, the wafer 200 includes a semiconductor-on-insulator (SOI)structure such as a buried dielectric layer. Alternatively, the wafer200 includes a buried dielectric layer such as a buried oxide (BOX)layer, such as that formed by a method referred to as separation byimplantation of oxygen (SIMOX) technology, wafer bonding, selectiveepitaxial growth (SEG), or other proper method.

In some embodiments, the semiconductor wafer 200 includes active and/orpassive devices formed thereon and therein. For example, doped regionsare formed in the semiconductor wafer 200 to define transistors. In someembodiments, dielectric and polysilicon layers are defined to form gatesof the transistors. In some embodiments, additional metal andpolysilicon layers are patterned to form interconnects between theactive and/or passive devices in and on the semiconductor wafer 200. Insome embodiments, other structures, such as through-substrate-vias(TSVs), post-passivation redistribution layers (PPI RDLs), and the likeare also formed on the semiconductor wafer 200. The various devices andinterconnect structures may primarily be formed on a front face 201 ofthe semiconductor wafer 200. In the polishing system 10, the front face201 may face toward polishing head 110, while a back face of thesemiconductor wafer 200 may face away from polishing head 110, and be incontact with the wafer table 120.

The wafer table 120 supports the wafer 200, and in some embodiments hasa wafer contacting surface made of a material such as silica gel. Forthe wafer 200 having the width w1, the wafer table 120 may be of widthgreater than the width w1 by at least 20 cm, for example. In someembodiments, the width w1 is in a range of about 25 millimeters to about450 millimeters. In some embodiments, the width w1 exceeds 450millimeters. Examples of the width w1 include 300 millimeters and 450millimeters.

The wafer table 120 may spin the semiconductor wafer 200 at a first rateand in a first direction. Spin variables of the semiconductor wafer 200,such as speed and direction, may be controlled by the rotation controlmechanism 121. In some embodiments, the rotation control mechanism 121is controlled by the system controller 140. In some embodiments, therotation control mechanism 121 causes rotation of the semiconductorwafer 200 through an electric motor. In some embodiments, the electricmotor is an alternating current (AC) motor, a direct current (DC) motor,a universal motor, or the like, and has fixed or variable speed. In someembodiments, the rotation control mechanism 121 includes electronics forsetting the speed of the electric motor. In some embodiments, theelectronics receive control signals from the system controller 140, andcontrol the speed of the electric motor in response to the controlsignals. In some embodiments, the control signals are real-time speedindication signals, and/or a spin rate profile specifying rotationspeeds of the semiconductor wafer 200 over time throughout a polishingprocess. Embodiments in which the rotation control mechanism 121 isoptional are also contemplated herein, for example when thesemiconductor wafer 200 is not rotated during polishing, but isstationary on the wafer table 120.

The polishing head 110 holds the polishing pad 111, and is controllableby the system controller 140 to apply pressure to the wafer 200 throughthe polishing pad 111. The system controller 140 is also capable oftranslating the polishing pad 111 through three dimensions as shown inFIG. 2, and also rotating the polishing pad 111 at a second rate and ina second direction. The polishing head 110 is controllable by the systemcontroller 140 (for example) to translate in the three dimensionsrelative to the front face 201. Two dimensions are indicated by crossingarrows in FIG. 2, with the third dimension being in and out of thefigure, orthogonal to the axes depicted by the crossing arrows. In someembodiments, the polishing pad 111 spins at the second rate and in thesecond direction (clockwise or counterclockwise), which is be the sameor different than the first rate and the first direction of the wafer200. In some embodiments, the second rate is fixed or variable, and isprogrammable and/or adjustable based on in-line metrology feedbackprovided by the metrology tools 130. In some embodiments, the secondrate is set in real-time by the system controller 140, and/or as apredefined profile specifying rotation rates and directions of thepolishing pad 111 over time throughout the polishing process.

A polishing surface of the polishing pad 111 faces toward the front face201 of the semiconductor wafer 200. In some embodiments, the polishingpad 111 polishes the semiconductor wafer 200 through a combination ofmechanical and chemical removal of layer material. In some embodiments,the polishing pad 111 is made of a polymer. The width w2 of thepolishing pad 111 is shorter than the width w1 of the semiconductorwafer 200. In some embodiments, the width w2 is less than half the widthw1. In some embodiments, the width w2 is between ¼ and ⅓ of the widthw1. In some embodiments, the polishing pad 111 is cylindrical in shape,with a circular cross-section relative to the plane of the front face ofthe wafer 200. Other shapes for the cross-section of the polishing pad111, including ovals, rectangles, squares, and the like, are alsocontemplated herein.

In some embodiments, the slurry delivery mechanism 122 mixes, storesand/or delivers chemical slurry to the front face 201 of the wafer 200to enable chemical mechanical polishing (CMP). In FIG. 1, the slurrydelivery mechanism 122 is shown as part of the wafer table 120. In someembodiments, the slurry delivery mechanism 122 is part of the polishinghead 110. In some embodiments, the chemical slurry is applied to thewafer 200 through the wafer table 120, and/or through the polishing pad111. For example, the chemical slurry is fed through a tube to thepolishing pad 111 through the polishing head 110. In some embodiments,the chemical slurry is also fed through a tube onto the front surface201 of the wafer 200 through a tube of the wafer table 120. In someembodiments, composition of the chemical slurry is controlled by theslurry delivery mechanism 122 according to a control signal generated bythe system controller 140. In some embodiments, the control signalprovides real-time composition control parameters, and/or a predefinedcomposition profile that is scheduled relative to the duration of thepolishing process. In some embodiments, other slurry variables, such asflow rate, are also controlled by the slurry delivery mechanism 122according to control signals generated by the system controller 140, inreal-time and/or in a predefined profile. In some embodiments, thevarious control signals related to slurry composition and other slurryvariables are generated as preset values, and/or in view of in-linemetrology data gathered by the metrology tools 130 during the polishingprocess.

The metrology tools 130 provide metrology information to the systemcontroller 140, including topography of the front face 201 of thesemiconductor wafer 200, for example. Thicknesses and contours of filmsand materials on the face of the semiconductor wafer 200 are measured bythe metrology tools 130, and transmitted to the system controller 140.The metrology tools 130 include a laser interferometer, for example.Based on the metrology information provided to the system controller140, in some embodiments, the system controller 140 controls variousprocess variables during the polishing process. Examples of processvariables controllable by the system controller 140 include rotationspeeds and directions of the wafer 200 and the polishing pad 111,location of the polishing head 110 over the wafer 200, force applied bythe polishing head 110 on the wafer 200, and slurry pumping rate and/orslurry composition of the slurry delivery mechanism 122. The use of themetrology tools 130 as described is referred to as intra-metrologyclosed loop control (IMCLC).

In some embodiments, a second polishing pad 112 is utilized in thepolishing system 10 to increase throughput as shown in FIGS. 3A and 3B.In FIG. 3A, according to some embodiments, the second polishing pad 112and the polishing pad 111 are collinear along center lines thereof, andseparated by a distance d1 (e.g., as measured from center of pad 112 tocenter of pad 111), which is about half the diameter w1 of thesemiconductor wafer 200. FIG. 3B shows a general case, in whichpositions of the polishing pads 111, 112 are defined in radialcoordinates. As such, the polishing pad 111 is located at a radius r1relative to the center of the wafer 200, and the polishing pad 112 islocated at a radius r2 relative to the center of the wafer 200. Theradii r1, r2 are further separated angularly by an offset angle θ. Inthe example shown in FIG. 3A, the offset angle θ is 180 degrees. Thevariables d1, r1, r2, and θ are all controllable by the systemcontroller 140, and in some embodiments, are set in a predeterminedpolishing profile, and/or in a real-time response to the in-linemetrology data provided by the metrology tools 130.

In some embodiments, cleaning is performed between polishing stages, andincludes use of brushes and cleaning agents (e.g., chemicals, deionized(DI) water). A cleaning unit 400 in accordance with various embodimentsof the present disclosure is shown in FIG. 4. In some embodiments, thecleaning unit 400 is a roller brush or disc brush, for example, and isconfigured to rotate and translate in at least one direction, asindicated by arrows to the right and above the cleaning unit 400 in FIG.4. In some embodiments, the semiconductor wafer 200 is held face up bythe wafer table 120, and is further rotated while the cleaning unit 400clears chemical slurry and particles from the face of the semiconductorwafer 200.

Based on the above, intermediate steps in a general polishing method 50are shown in FIG. 5. Described in terms of FIGS. 1-2, 3A-3B, and 4, thepolishing method 50 includes a first polishing process performed inblock 500, a first cleaning process performed in block 501, a secondpolishing process performed in block 502, and a second cleaning processperformed in block 503. It is understood that the second polishing andcleaning processes or the first polishing and cleaning processes areoptional in some embodiments. Order of the blocks 500-503 may also bechanged to form various embodiments, all of which are contemplatedherein. For example, blocks 502 and 503 are performed prior to blocks500 and 501 in some embodiments.

One polishing head is used to polish the wafer 200 in block 500. In someembodiments, the polishing head is of a first type (e.g., Type 1), andis used with a first chemical slurry (e.g., Type A). In someembodiments, a first profile P1 is used that defines polishing speeds,polishing pressures, polishing positions, durations, slurry compositionand flow rate, and the like, as described above.

Following block 500, the first cleaning process is performed in block501. A first cleaner, such as a brush (e.g., Brush 1), is used with afirst cleaning agent (e.g., Agent M) to clean the polished surface ofthe wafer 200 by the first cleaning process in block 501. In someembodiments, the cleaning agent is selected in accordance with thechemical slurry used in block 500. In some embodiments, a cleaningprofile C1 defines rotation speeds, positions, durations, flow rates,and the like to provide sufficient and/or optimal cleaning of the wafer200.

Two polishing heads are used in block 502. In some embodiments, thepolishing heads are the same or a different type (e.g., Type 2 and Type3), and are used with a chemical slurry of a type (e.g., Type B) that isthe same or different from the type of the chemical slurry used in theblock 500. In some embodiments, a second polishing profile P2 is definedfor use with the polishing heads and slurry of block 502, which definespolishing rates, flow rates, polishing positions of the polishing heads(e.g., radii and angular separation), durations, pressures, and thelike.

A second cleaning process is performed in block 503 to clear awayresidual slurry from the polishing process in block 502. In someembodiments, a second cleaner (e.g., Brush 2) is used with a secondcleaning agent (e.g., Agent N) in accordance with a second cleaningprofile C2 to remove the residual slurry. In some embodiments, thesecond cleaner is the same or different from the first cleaner, andcleaners other than brushes are also contemplated herein. In someembodiments, the second cleaning agent is the same or different from thefirst cleaning agent, and is selected in accordance with the chemicalslurry used in block 502. The cleaning profile C2 may define rotationspeeds, positions, durations, flow rates, and the like to providesufficient and/or optimal cleaning of the wafer 200.

In some embodiments, the cleaning processes in blocks 501 and 503described above utilize the cleaning unit 400. In some embodiments, thecleaning unit 400 is spun and lowered onto the semiconductor wafer 200surface, and pressure is applied to the cleaning unit 400 toward theface of the semiconductor wafer 200. In some embodiments, the cleaningunit 400 begins cleaning at an edge of the semiconductor wafer 200, suchas the bottom edge shown in FIG. 4, and is translated toward an oppositeedge in a single direction, for example. Embodiments where the cleaningunit 400 is pivoted from one end thereof to swipe angularly across theface of the semiconductor wafer 200 are also contemplated herein. Insome embodiments, a cleaning chemical solution and/or DI water isdeposited on the face of the semiconductor wafer 200 to aid in removingall residue from the semiconductor wafer 200.

The polishing system 10 using the polishing head 110 saves space overtraditional polishing systems. The polishing pads 111, 112 allow fornumerous polishing profiles to be used, and in some embodiments are tiedin with the in-line metrology data provided by the metrology tools 130to provide automated profile adjustment without taking the semiconductorwafer 200 offline. The cleaning unit 400 in the polishing system 10 alsosaves time, eliminating the need for offline cleaning stations. In someembodiments, the semiconductor wafer 200 is polished and cleaned in thesame station, which saves space and greatly reduces wafer transfer time.The polishing system 10 saves space and time, and has flexible polishingprofile control, which translates into an increase in both yield andthroughput.

A polishing system 60 in accordance with various embodiments of thepresent disclosure is shown in FIG. 6. A main polishing pad 600 forpolishing a wafer has a polishing face, which is made of polyurethane,for example. The main polishing pad 600 is rotated at a constant speed,or at a variable speed determined by a system controller 620. Therotation is controlled by a motor 605 that drives the main polishing pad600, for example. The variable speed controlled based on a signal 622sent to the motor 605 from the system controller 620, and the motor 605may vary the rotational speed of the main polishing pad 600 in responseto the signal. The main polishing pad 600 may rotate in a clockwisedirection or a counter-clockwise direction. The main polishing pad 600is circular, for example, and has a diameter greater than asemiconductor wafer to be polished. In some embodiments, the diameter ofthe main polishing pad 600, D_(PAD), is at least two times as long asthe diameter of the semiconductor wafer, D_(WAFER). Exemplary mainpolishing pad diameter for a 450 mm semiconductor wafer is about 1094 mm(D_(PAD)/D_(WAFER) approximately 2.43), compared with main polishing paddiameter of about 762 mm for 300 mm wafers (D_(PAD)/D_(WAFER)approximately 2.54) and main polishing pad diameter of about 508 mm for200 mm wafers (D_(PAD)/D_(WAFER) approximately 2.54).

A polishing head 610, shown in detail in FIG. 7, presses a wafer 700,such as a semiconductor wafer, against the main polishing pad 600. Thesemiconductor wafer 700 has width w₁ which is typically shorter thanhalf width w₃ of the main polishing pad 600, as described above. Thepolishing head 610 has a retainer ring 614 installed in a frame 612thereof. The retainer ring 614 is made of polyphenylene sulfide (PPS),polyether ether ketone (PEEK) or another suitable polyimide orthermoplastic material, and holds the semiconductor wafer 700 by anedge/bezel region of the semiconductor wafer 700. In some embodiments,the polishing head 610 applies a general force on the semiconductorwafer 700 toward the main polishing pad 600. Applicators 615-618 providelocalized pressure at various regions of the semiconductor wafer 700 tochange the contour of the semiconductor wafer 700, and control polishingrates of the various regions of the semiconductor wafer 700. Theapplicator 615 applies pressure to a center zone of the semiconductorwafer 700, the applicator 616 applies pressure to a ripple zone of thesemiconductor wafer 700, the applicator 617 applies pressure to an outerzone of the semiconductor wafer 700, and the applicator 618 appliespressure to an edge zone of the semiconductor wafer 700, as shown inFIG. 7. The pressures applied are mechanical, pneumatic, fluid, or thelike, and are controllable by the system controller 620.

In some embodiments, in addition to pressing the semiconductor wafer 700against the main polishing pad 600, the polishing head 610 furtherrotates in a direction the same or opposite that of the main polishingpad 600. In some embodiments, the main polishing pad 600 rotatesclockwise, while the polishing head 610 rotates counterclockwise, forexample. In some embodiments, the main polishing pad 600 rotatesclockwise, while the polishing head 610 also rotates clockwise. In someembodiments, rotation of the polishing head 610 is controlled by a motor670 that drives the polishing head 610. In some embodiments, the motor670 rotates the polishing head 610 at a constant speed, or at a variablespeed controllable by the system controller 620. In some embodiments,the polishing head 610 is also subject to translation in a planecoplanar to the face of the main polishing pad 600. In some embodiments,the translation is controllable by the system controller 620, and isprogrammed into the polishing system 60 as part of a predefinedpolishing profile.

In some embodiments, the polishing system 60 is a chemical mechanicalpolishing (CMP) system, for example. In some embodiments, a slurrydelivery system 640 releases a chemical slurry onto the main polishingpad 600 surface at a constant rate, or a variable rate determined by thesystem controller 620. In some embodiments, the slurry delivery system640 includes a pump, and a tube installed in the main polishing pad 600.In some embodiments, the chemical slurry includes silica solids,chemical dispersants, surfactants, and the like. In some embodiments,composition of the chemical slurry is also controllable by the systemcontroller 620. In some embodiments, the system controller 620 controlsslurry delivery parameters, such as delivery rate and slurry compositionthrough a signal 623.

Metrology tools 630 provide metrology information to the systemcontroller 620, including topography of the face of the semiconductorwafer 700, for example. Thicknesses and contours of films and materialson the face of the semiconductor wafer 700 are measured by the metrologytools 630, and transmitted to the system controller 620. The metrologytools 630 include a laser interferometer, for example. In someembodiments, based on the metrology information provided to the systemcontroller 620, the system controller 620 controls rotation speeds ofthe main polishing pad 600 and the polishing head 610, location of thepolishing head 610 over the main polishing pad 600, force applied by thepolishing head 610, pressure levels of the applicators 615-618, andslurry pumping rate and/or slurry composition of the slurry deliverysystem 640. The use of the metrology tools 630 as described is referredto as intra-metrology closed loop control (IMCLC).

The system controller 620 controls the main polishing pad 600, thepolishing head 610, and the slurry delivery system 640 to perform afirst polishing process. In some embodiments, the first polishingprocess is based on a first predefined polishing profile, whichspecifies polishing time, as well as polishing variables including, butnot limited to, rotation speeds of the main polishing pad 600 and thepolishing head 610, translation of the polishing head 610, force of thepolishing head 610, regional pressure levels of the applicators 615-618,and slurry rate and composition variables of the slurry delivery system640 as a function of time. In some embodiments, rotation speed of thepolishing head 610 varies over the duration of the first polishingprocess. In some embodiments, a path is set for the polishing head 610to use the entire area of the main polishing pad 600 through the firstpolishing process, for example. In some embodiments, the first polishingprocess is adaptive, making use of the IMCLC to control the polishingvariables in response to metrology metrics including, but not limitedto, layer thickness and layer smoothness.

Upon completion of the first polishing process, metrology data providedby the metrology tools 630 may indicate that at least one zone of theface of the semiconductor wafer 700 under process is not evenlypolished. FIGS. 8-13 are illustrations of wafer contours 711-716following completion of the first polishing process. In FIG. 8, acentral region of the semiconductor wafer 700 is polished less, e.g. hasgreater layer thickness, than outer and edge regions of thesemiconductor wafer 700. This may indicate that the applicator 615 isdefective, damaged, aging, or requires maintenance. In FIG. 9, thesemiconductor wafer contour 712 may indicate that the ring zone of thesemiconductor wafer 700 is underpolished relative to other zones of thesemiconductor wafer 700. The applicator 616 is defective, damaged,aging, or require maintenance, for example. The semiconductor wafercontours 713 and 714 in FIG. 10 and FIG. 11, respectively, indicateunderpolishing in the outer zone and the edge zone, which may correspondto improper function of the applicators 617 and 618. The semiconductorwafer contour 715 in FIG. 12 corresponds to underpolishing in two zones,such as the ring zone and the edge zone. Other two-zone contours mayinclude underpolishing in the center zone and the outer zone, andunderpolishing in the center zone and the edge zone. A wafer contour 716shown in FIG. 13 corresponds to a case in which at least one area of thesemiconductor wafer 700 has, for example, higher thickness thanoriginally programmed into the polishing system 60 for the firstpolishing process. The high thickness(es) is die localized in FIG. 13,affecting, for example, a single die, or at least two adjacent dieslocated in a roughly circular or other shaped region that isnon-concentric to the semiconductor wafer 700.

An auxiliary polishing system 650 installed in the polishing system 60is shown in FIG. 6, and a detailed view thereof is shown in FIG. 14. Insome embodiments, the polishing head 610 serves dual purposes in thepolishing system 60. In the first polishing process (main polishingprocess), the polishing head 610 holds the semiconductor wafer 700,presses the semiconductor wafer 700 against the main polishing pad 600,spins the semiconductor wafer 700, translates the semiconductor wafer700 over the face of the main polishing pad 600, and performs zonepolish control through the applicators 615-618. In a second polishingprocess (auxiliary polishing process), as part of the auxiliarypolishing system 650, the polishing head 610 acts as a table holding thesemiconductor wafer 700 toward auxiliary polishing units 651 and 652,while at least one auxiliary polishing unit 651, 652, polishes at leastone zone and/or at least one area of the semiconductor wafer 700. In thesecond polishing process, the polishing head 610 holds the semiconductorwafer 700, spins the semiconductor wafer 700, and/or translates thesemiconductor wafer 700 in three dimensions.

Two auxiliary polishing units 651, 652 are shown in FIG. 14. Embodimentsincluding only one, two, three, or more than three auxiliary polishingunits are contemplated herein. An auxiliary polishing pad 653 of theauxiliary polishing unit 651 is attached to an axle 654, which isattached to an auxiliary controller 655. In some embodiments, apolishing surface of the auxiliary polishing pad 653 includes materialsimilar to the material of the main polishing pad 600, such aspolyurethane. A polishing surface of the auxiliary polishing pad 653 iscircular, for example. Width of the polishing surface of the auxiliarypolishing pad 653, which may also be diameter for a circular shape, isindicated as width w₂ in FIG. 14. The width w₂ of the polishing surfaceof the auxiliary polishing pad 653 is shorter than the width w₁ of thesemiconductor wafer 700. The width w₂ is shorter than about half thewidth w₁, for example. The width w₂ is between about ¼ to about ⅓ of thewidth w₁, or even shorter than about ¼ of the width w₁. Width of apolishing face of a second auxiliary polishing pad 657 of the auxiliarypolishing unit 652, which may also be diameter for a circular shape, isindicated as width w₄ in FIG. 14. The width w₄ is shorter than the widthw₁ of the semiconductor wafer 700, and in some embodiments is about thesame as the width w₂. In some embodiments, the width w₄ is differentfrom the width w₂ of the auxiliary polishing pad 653. In someembodiments, the auxiliary polishing pad 657 has the same shape as, or adifferent shape than, the auxiliary polishing pad 653. In someembodiments, polishing surfaces of the auxiliary polishing pads 653,657, which are affected by polishing material and/or texturing, are thesame or different.

In some embodiments, the auxiliary controller 655, which controls theauxiliary polishing units 651, 652 to perform the second polishingprocess, includes electronics, and electrical and mechanical systems forcontrolling rotation of the axles 654, 658 and the auxiliary polishingpads 653, 657 and for controlling translation of the axles 654, 658 andthe auxiliary polishing pads 653, 657 in three dimensions before,during, and after the second polishing process. In some embodiments, theauxiliary controller 655 includes motors for spinning the auxiliarypolishing units 651, 652. In some embodiments, the motors are controlledelectronically to spin at variable and/or constant speeds before,during, and after the second polishing process. In some embodiments, theauxiliary controller 655 further includes levers and/or pistons forapplying downward force on the auxiliary polishing units 651, 652 toapply pressure on the zone(s) and/or area(s) to be polished in thesecond polishing process.

A signal line (or bus) 661 electrically connects the auxiliarycontroller 655 to the metrology tools 630, so that the auxiliarycontroller 655 automatically translates metrology data (layer thickness,contour profile) of the semiconductor wafer 700 into polishing steps ofthe second polishing process. Configurations in which the auxiliarycontroller 655 is electrically connected to the system controller 620are also contemplated herein. In some embodiments, the system controller620 interprets the metrology data from the metrology tools 630, andsends polishing commands to the auxiliary controller 655, such that theauxiliary controller 655 need not be directly electrically connected tothe metrology tools 630 to perform the second polishing process. In sucha configuration, in some embodiments, the auxiliary controller 655 doesnot include interpreter hardware and/or software for intelligentlyhandling feedback data from the metrology tools 630, but relies on thesystem controller 620 for polishing variables, such as spin rates,pressures, stutter rates, and/or displacements and paths for theauxiliary polishing units 651, 652. In some embodiments, the systemcontroller 620 includes hardware (e.g., a processor, memory, logiccircuits, and the like).

For a chemical mechanical polishing (CMP) system, the second polishingprocess includes introduction of a chemical slurry, such as thatdescribed above, on the face of the semiconductor wafer 700 underprocess. The chemical slurry is introduced in various ways. As oneexample, an auxiliary slurry delivery system 670 shown in phantom inFIG. 14 may deliver the chemical slurry to the face of the semiconductorwafer 700 through a tube and a pump. In some embodiments, the auxiliaryslurry delivery system 670 is installed in and through the polishinghead 610, with evenly spaced outlets along a radius of the face of thepolishing head 610, for example. Another slurry delivery system isintegral to the auxiliary polishing units 651, 652, where the chemicalslurry is delivered into the auxiliary polishing pads 653, 657 throughtubes 656, 659, for example. In some embodiments, the two deliverysystems are used individually or in conjunction to introduce thechemical slurry onto the face of the semiconductor wafer 700 duringpolishing of the zone(s) and/or area(s) in the second polishing process.In some embodiments, the auxiliary controller 655 is configured tocontrol slurry variables, including delivery rate(s), slurry mix ratios,and the like of the chemical slurry delivered by any or all of thedelivery systems 670, 656, and 659 described herein. In someembodiments, the slurry variables are controlled by the systemcontroller 620, for example.

In some embodiments, the polishing head 610 is configured to be rotated,so that the face of the semiconductor wafer 700 under process can faceaway from the main polishing pad 600 during the second polishingprocess. For example, the polishing head 610 is rotated 180 degrees, sothat the polishing head 610 is inverted relative to its originalposition during the first polishing process. Other angles of rotationare also contemplated, such as 90 degrees clockwise or counterclockwise.In some embodiments, a first positioning mechanism 680 (FIG. 6) rotatesthe polishing head 610 away from the main polishing pad 600, forexample, so that the polishing head 610 faces up. In some embodiments,the face of the semiconductor wafer 700 after rotating the polishinghead 610 away from the main polishing pad 600 has substantially the sameorientation as the face of the main polishing pad 600. In someembodiments, the face of the polishing head 610 is oriented in such away that a surface normal (normal vector) thereof is substantiallyparallel to and opposite the direction of gravity, for example.Orientations at a slight tilt from parallel are also contemplated, whichmay aid drainage of chemical slurry from the semiconductor wafer 700.

In some embodiments, the polishing head 610 is further rotated and/ortranslated away from the main polishing pad 600, such that the polishinghead 610 is not directly above the main polishing pad 600. In someembodiments, the translating is performed by the first positioningmechanism 680, and the rotating is performed by a second positioningmechanism 690 connected to the first positioning mechanism 680 accordingto a signal 621, for example. Moving the polishing head 610 away fromthe main polishing pad 600 allows the main polishing pad 600 to continueprocessing subsequent wafers under precise slurry volume control withoutexcess slurry dripping onto the main polishing pad 600 from above as thepolishing head 610 is involved in the second polishing process.Configurations in which multiple polishing heads 610 are included in thepolishing system 60 to accommodate for a higher numbers of wafers underprocess are contemplated herein. Whereas a traditional polishing systemmay include three polishing pads and three polishing heads, for example,a polishing system similar to the polishing system 60 may include threepolishing pads and six polishing heads, so as not to reduce throughputas each wafer is polished twice.

Embodiments in which the auxiliary polishing system 650 includes thecleaning sub-system 400 shown in FIG. 4 are also contemplated herein.

Flowcharts of a full polishing process 1500 and a second polishingprocess 1600 in accordance with various embodiments of the presentdisclosure are shown in FIG. 15 and FIG. 16, respectively. Thesemiconductor wafer 700 is initially polished using a first polishingprofile in block 1510, which is considered a first polishing process bya first polishing pad having a width greater than the semiconductorwafer 700. The first polishing process is completed using the polishinghead 610 and the main polishing pad 600, as described above. Thesemiconductor wafer 700 is then transferred to an auxiliary polishingsystem, such as the auxiliary polishing system 650 shown in FIG. 6 andFIG. 14, in block 1520. An auxiliary polishing pad, such as theauxiliary polishing pad 653 of the auxiliary polishing unit 651 shown inFIG. 14 is used to polish the semiconductor wafer 700 according to asecond polishing profile in block 1530, which is considered a secondpolishing process by an auxiliary polishing pad having a width less thanthe semiconductor wafer 700.

In some embodiments, the second polishing process 1600 shown in FIG. 16is the same as the block 1530 in FIG. 15. In some embodiments, thesecond polishing process 1600 shown in FIG. 16 begins after completingthe first polishing process, and transferring the semiconductor wafer700 to the auxiliary polishing system 650 in block 1520, for example. Insome embodiments, metrology data, such as the metrology data generatedby the metrology tools 630 shown in FIG. 6 is received by the systemcontroller 620 and/or the auxiliary controller 655 in block 1610. Insome embodiments, the metrology data is received after completion of thefirst polishing process. In accordance with various embodiments of thepresent disclosure, the metrology data is received at any time duringthe full polishing process 1500, such as during the first polishingprocess, or during the transferring of the semiconductor wafer 700 tothe auxiliary polishing system 650. As described above, in someembodiments, the metrology data includes characteristics including layerthickness contours, and/or layer roughness data. In some embodiments,the characteristics are mapped to coordinates of the semiconductor wafer700.

In block 1620, the received metrology data is analyzed to determineimproperly polished regions of the semiconductor wafer 700. In someembodiments, the improperly polished regions exhibit thickness and/orsurface texture that differs from expected thickness and/or textureprogrammed into the first predefined polishing profile. In someembodiments, using standard techniques, such as edge detection, theimproperly polished regions of the semiconductor wafer 700 isdetermined. In some embodiments, the metrology data is pixel-level data,such that the improperly polished regions is pixel-sized at a finestgranularity. Using image processing techniques, the pixel-sized regionsare grouped into larger regions in some embodiments, such as the ringzones described in reference to FIGS. 8-12, or the localized areas shownin FIG. 13. As an example, a ring zone is loosely defined by an innerradius and an outer radius. Then, a central radius, or track, isobtained by averaging the inner and outer radii, for example. Width ofthe track is obtained by subtracting the inner radius from the outerradius, for example. Thus, on a 300 mm wafer, a track of width about 40mm and center radius about 90 mm is found corresponding to an innerradius of about 70 mm and an outer radius of about 110 mm, as only oneexample. In some embodiments, the track corresponds to one or more ofthe applicators 615-618, such as the outer zone applicator 617, forexample.

In some embodiments, the improperly polished region(s) has defined shapeand contour, and a second predefined polishing profile is generatedaccordingly in block 1630 to improve planarity and/or surface smoothnessuniformity over the semiconductor wafer 700 surface. Taking again theexample of a ring zone, having found a track width and center radius ofthe ring zone, a second polishing profile that defines position of theauxiliary polishing pad, applied pressure(s), and/or polishing time andthe like is generated to planarize and/or smooth the improperly polishedring zone.

In accordance with various embodiments of the present disclosure,auxiliary polishing pads of the auxiliary polishing system 650 havedifferent sizes. For example, auxiliary polishing pad widths range fromabout 25 mm to about 100 mm. In some embodiments, the track width istaken into consideration when selecting the auxiliary polishing pad.Using the previous example of a track width of 40 mm, an auxiliarypolishing pad of width greater than 40 mm and shorter than about 70 mmis selected manually or automatically as part of the second polishingprofile. In some embodiments, auxiliary polishing pads of the auxiliarypolishing system 650 all have the same size, and no selection based onpad size, either automatic or manual, need be performed. Embodiments inwhich the auxiliary polishing pads have different polishing surfaces,such as different polishing materials, and are selectable according topolishing material defined in the desired second polishing profile, arealso contemplated herein.

Using the second polishing profile generated according to block 1630 ofFIG. 16, in some embodiments the auxiliary polishing system 650 polishesthe improperly polished region(s) in block 1640. To polish thesemiconductor wafer 700, the auxiliary polishing system 650 spins thesemiconductor wafer 700 and spins the auxiliary polishing pad(s) 653,657. The auxiliary polishing system 650 further positions the auxiliarypolishing pad(s) 653, 657 over the improperly polished region(s), andlowers the auxiliary polishing pad(s) 653, 657 until contact is madewith the semiconductor wafer 700. Chemical slurry is applied, and/orpressure is varied between the auxiliary polishing pad(s) 653, 657 andthe semiconductor wafer 700. The above steps are not necessarilyperformed in the order described. In some embodiments, the auxiliarypolishing system 650 holds the semiconductor wafer 700 while theauxiliary polishing pad(s) 653, 657 polish the semiconductor wafer 700.For the localized areas shown in FIG. 13, holding the semiconductorwafer 700 stationary is preferable, and the auxiliary polishing pads653, 657 are positioned over centers of the localized areas, or aretranslated in patterns to provide uniform polishing coverage over thelocalized areas. For two or more improperly polished regions, theimproperly polished regions are polished simultaneously, sequentially,or a combination of the two (for three or more improperly polishedregions).

In some embodiments, the localized areas in FIG. 13 are polished whilethe semiconductor wafer 700 is spinning. Knowing the spin rate of thesemiconductor wafer 700, radii corresponding to centers of the localizedareas, and radial lengths of the localized areas, stutter frequenciesare calculated, such that the auxiliary polishing pad(s) 651, 652 remainmostly stationary, and apply short bursts of pressure as the localizedarea(s) pass by the auxiliary polishing pad(s) 651, 652. For example, ifan improperly polished area has a center located at an 80 mm radius fromthe center of the semiconductor wafer 700, and average radius of 15 mm,and the semiconductor wafer 700 is spun at 60 revolutions per minute(rpm), the improperly polished area passes the auxiliary polishing pad651 (for example) once per second. The auxiliary polishing pad 651 isthen lowered and raised with a stutter frequency of 1 Hz. Contact timefor each pulse in which the auxiliary polishing pad 651 is appliedpressure to polish the face of the semiconductor wafer 700 is set invarious manners, including time required for the improperly polishedarea to pass the area of the auxiliary polishing pad 651. If radius ofthe auxiliary polishing pad 651 is about 25 mm, time for the improperlypolished area to pass through the length of the auxiliary polishing padis approximated to about D_(PAD)/V_(CENTER), where D_(PAD) is diameterof the auxiliary polishing pad 651 (50 mm in the example given), andV_(CENTER) is linear velocity of the center of the improperly polishedarea. In the example given, D_(PAD) is 50 mm (25 mm*2), and V_(CENTER)is about 503 mm/s (2*π*80 mm/s), which gives a pulse width ofapproximately 1/10 second, or 100 milliseconds.

The second polishing process 1600 is performed as part of the fullpolishing process 1500, as described above. In accordance with variousembodiments of the present disclosure, the second polishing process 1600is performed independently, for example as part of a batch reworksystem, where the metrology data is saved in a server or portablestorage medium, for example, and downloaded from the server duringrework (the second polishing process) of the semiconductor wafer 700. Insome embodiments, the auxiliary polishing system 650 is part of thepolishing system 60. In some embodiments, the auxiliary polishing system650 is an independent polishing system, such as a rework station, forexample. In such an independent polishing system, a polishing headsimilar to the polishing head 610 is utilized to hold the semiconductorwafer 700. In some embodiments, a wafer table is utilized to hold thesemiconductor wafer 700 while auxiliary polishing units similar to theauxiliary polishing units 651, 652 perform a second polishing process onthe semiconductor wafer 700. This type of configuration is appropriatewhen the semiconductor wafer 700 is to be taken offline prior toundergoing the second polishing process.

In FIGS. 6 and 14, the polishing head 610 is shown facing up, while theauxiliary polishing units 651, 652 face down. Embodiments in which thepolishing head 610 faces down, while the auxiliary polishing units 651,652 face up are also contemplated herein. In this configuration, thepolishing head 610 lifts the semiconductor wafer 700 from the mainpolishing pad 600, translates the semiconductor wafer 700 to a positionover the auxiliary polishing units 651, 652, and lowers thesemiconductor wafer 700 and/or raises the auxiliary polishing units 651,652 to make contact and polish the semiconductor wafer 700 through thesecond polishing process described above. No rotation of the polishinghead 610 is required in such a configuration.

Embodiments where the polishing system 60 does not include the mainpolishing pad 600 and the auxiliary polishing system 650 polishes theentire face of the semiconductor wafer 700 are contemplated herein. Insome embodiments, the auxiliary polishing pad 651 has a width similar tothe width of the semiconductor wafer 700, for example. Then, block 1510of FIG. 15 is modified to use the auxiliary polishing pad 651 having thewidth similar to the width of the semiconductor wafer 700. Block 1520 isremoved from the full polishing process 1500, and a second auxiliarypolishing pad, such as the auxiliary polishing pad 652, having widthshorter than the width of the semiconductor wafer 700 is used to polishthe semiconductor wafer 700 using the second predefined polishingprofile.

In some embodiments, the auxiliary polishing system 650 is also used asa bevel polisher in accordance with various embodiments of the presentdisclosure. An auxiliary bevel polishing unit 1700 and bevel polishingscheme are depicted in FIGS. 17 to 20. The auxiliary bevel polishingunit 1700 includes a bevel polishing pad 1701. To polish a bevel region701 of the semiconductor wafer 700, the auxiliary bevel polishing unit1700 spins the bevel polishing pad 1701 as shown in FIG. 17. Thespinning bevel polishing pad 1701 is translated toward the semiconductorwafer 700 to make contact with the bevel region 701 as shown in FIG. 18.In some embodiments, a lower inclined portion of the bevel polishing pad1701 having a first angle θ1 relative to the face of the semiconductorwafer 700 polishes the bevel region 701 first. Subsequently, as shown inFIG. 19, the bevel polishing pad 1701 is translated downward, such thatan upper inclined portion of the bevel polishing pad 1701 having asecond angle θ2 relative to the face of the semiconductor wafer 700polishes the bevel region 701. In some embodiments, the bevel polishingpad 1701 is moved toward the center of the semiconductor wafer 700 tobring the bevel region 701 of the semiconductor wafer 700 back to themeeting point of the upper and lower inclined portions, then moved up topolish the bevel region 701 by the lower inclined portion again. In someembodiments, these steps are iterated prior to translating the bevelpolishing pad 1701 away from the semiconductor wafer 700 as shown inFIG. 20. Embodiments where the bevel polishing pad 1701 and theauxiliary polishing pad 651 are the same pad are also contemplatedherein. For example, a downward-facing surface of the auxiliarypolishing pad 651 polishes the face of the semiconductor wafer 700, anda side surface of the same auxiliary polishing pad 651 polishes thebevel of the semiconductor wafer 700.

The polishing system 60 including the auxiliary polishing system 650, byusing the polishing head 610 as a portable wafer table, saves space andrework time over traditional polishing systems. The auxiliary polishingunits 651, 652 of the auxiliary polishing system 650 allow for numerouspolishing profiles to be used, and can be tied in with the metrologydata provided by the metrology tools 630 to provide automated, in linerework without taking the semiconductor wafer 700 offline. The auxiliarybevel polishing unit 1200 and the cleaning unit 1600 in the auxiliarypolishing system 650 also save time, eliminating the need for offlinebevel polishing and cleaning stations. The semiconductor wafer 700 canbe polished, bevel polished, and cleaned in the same station, whichsaves space and greatly reduces wafer transfer time. The polishingsystem 60 saves space and time, and has flexible polishing profilecontrol, which translates into an increase in both yield and throughput.

One aspect of this description relates to a polishing system. Thepolishing system includes a wafer support for holding a wafer, the waferhaving a first diameter. The polishing system further includes a firstpolishing pad for polishing a first region of the wafer, the firstpolishing pad having a second diameter greater than the first diameter.The polishing system further includes an auxiliary polishing systemcomprising at least one second polishing pad for polishing a secondregion of the wafer, wherein the second polishing pad has a thirddiameter less than the first diameter, and the wafer support isconfigured to support the wafer during use of the first polishing padand the auxiliary polishing system. In some embodiments, the wafersupport is a wafer table. In some embodiments, the wafer support is apolishing head. In some embodiments, the polishing system furtherincludes a pad positioning mechanism for moving the first polishing padin three dimensions relative to a surface of the semiconductor wafer. Insome embodiments, a slurry supply system for introducing slurry to thefirst polishing pad. In some embodiments, the first polishing pad is abevel polishing pad, and the region is a bevel of the wafer. In someembodiments, the second region is a ring region approximately concentricto the semiconductor wafer and having an outer radius shorter than anouter radius of the wafer. In some embodiments, the third diameter isshorter than or equal to about one quarter the second diameter. In someembodiments, the first region is a first ring region approximatelyconcentric to the wafer; the second region is a second ring regionapproximately concentric to the wafer; and the first ring region and thesecond ring region are non-overlapping. In some embodiments, thepolishing system further includes a cleaning system for cleaning theregion of the semiconductor wafer.

Another aspect of this description relates to a polishing system. Thepolishing system includes a wafer support for holding a wafer. Thepolishing system further includes a first polishing pad for polishing afirst region of the wafer. The polishing system further includes anauxiliary polishing system for polishing a second region of the wafer,wherein the auxiliary polishing system includes a second polishing padhaving a diameter less than a diameter of the first polishing pad, andthe wafer support is configured to hold the wafer during operation ofboth the first polishing pad and the auxiliary polishing system. Thepolishing system further includes a controller connected to theauxiliary polishing system, wherein the controller is configured todetermine a location of the second region of the wafer based on athickness profile of the wafer. In some embodiments, the polishingsystem further includes a metrology tool connected to the controller,wherein the metrology tool is configured to measure the thicknessprofile of the wafer. In some embodiments, the polishing system furtherincludes a positioning mechanism connected to the wafer support. In someembodiments, the positioning mechanism is configured to rotate the wafersupport into a first position and into a second position, and the wafersupport in the first position is rotated 180-degrees with respect to thewafer support in the second position. In some embodiments, the wafersupport in the first position is configured to press the wafer againstthe first polishing pad. In some embodiments, the wafer support in thesecond position is configured to press the wafer against the auxiliarypolishing system.

Still another aspect of this description relates to a polishing system.The polishing system includes a wafer support for holding a wafer. Thepolishing system further includes a first polishing pad for polishing afirst region of the wafer. The polishing system further includes anauxiliary polishing system for polishing a second region of the wafer.The polishing system further includes a controller connected to thewafer support, wherein the controller is configured to control aposition of the wafer support for moving the wafer support between afirst position for bring the wafer in contact with the first polishingpad and a second position for bringing the wafer in contact with theauxiliary polishing system. In some embodiments, the controller isfurther configured to control supply of a slurry to the first polishingpad. In some embodiments, the polishing system further includes ametrology tool configured to measure a thickness profile of the wafer.In some embodiments, the controller is configured to determine alocation of the second region based on the measured thickness profile ofthe wafer.

Although the present embodiments and their advantages have beendescribed in detail, it should be understood that various changes,substitutions, and alterations can be made herein without departing fromthe spirit and scope of the disclosure as defined by the appendedclaims. Moreover, the scope of the present application is not intendedto be limited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods, and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the disclosure, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed, that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the present disclosure.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps.

What is claimed is:
 1. A polishing system comprising: a wafer supportconfigured to hold a wafer, the wafer having a first diameter; a firstpolishing pad configured to polish a first region of the wafer, thefirst polishing pad having a second diameter greater than the firstdiameter; an auxiliary polishing system comprising at least one secondpolishing pad that polishes a second region of the wafer, wherein thesecond polishing pad has a third diameter less than the first diameter,the third diameter is shorter than or equal to about one quarter thesecond diameter, and the wafer support is configured to support thewafer during use of the first polishing pad and the auxiliary polishingsystem; and a positioning mechanism connected to the wafer support,wherein the positioning mechanism is configured to rotate the wafersupport about an axis perpendicular to an axis of rotation of the firstpolishing pad.
 2. The polishing system of claim 1, wherein the wafersupport is a wafer table.
 3. The polishing system of claim 1, whereinthe wafer support is a polishing head.
 4. The polishing system of claim1, further comprising: a pad positioning mechanism that moves the firstpolishing pad in three dimensions relative to a surface of thesemiconductor wafer.
 5. The polishing system of claim 1, furthercomprising: a slurry supply system that introduces slurry to the firstpolishing pad.
 6. The polishing system of claim 1, wherein the secondregion is a ring region approximately concentric to the semiconductorwafer and having an outer radius shorter than an outer radius of thewafer.
 7. The polishing system of claim 1, wherein: the first region isa first ring region approximately concentric to the wafer; the secondregion is a second ring region approximately concentric to the wafer;and the first ring region and the second ring region arenon-overlapping.
 8. The polishing system of claim 1, further comprisinga cleaning system that cleans the semiconductor wafer.
 9. The polishingsystem of claim 1, wherein the auxiliary polishing system is separatedfrom the first polishing pad in a direction parallel to an axis ofrotation of the first polishing pad.
 10. The polishing system of claim1, wherein the auxiliary polishing system comprises a plurality ofsecond polishing pads.
 11. A polishing system comprising: a wafersupport configured to hold a wafer; a first polishing pad configured topolish a first region of the wafer; an auxiliary polishing systemconfigured to polish a second region of the wafer, wherein the auxiliarypolishing system comprises a second polishing pad having a diameter lessthan a diameter of the first polishing pad, and the wafer support isconfigured to hold the wafer during operation of both the firstpolishing pad and the auxiliary polishing system; a positioningmechanism connected to the wafer support, wherein the positioningmechanism is configured to rotate the wafer support about an axisperpendicular to an axis of rotation of the first polishing pad; ametrology tool configured to measure a thickness profile of the wafer;and a controller communicatively coupled to the auxiliary polishingsystem, wherein the controller is configured to determine a location ofthe second region of the wafer based on the measured thickness profileof the wafer.
 12. The polishing system of claim 11, wherein themetrology tool is connected to the controller.
 13. The polishing systemof claim 11, wherein the positioning mechanism is configured to rotatethe wafer support into a first position and into a second position, andthe wafer support in the first position is rotated 180-degrees withrespect to the wafer support in the second position.
 14. The polishingsystem of claim 11, wherein the wafer support in the first position isconfigured to press the wafer against the first polishing pad.
 15. Thepolishing system of claim 11, wherein the wafer support in the secondposition is configured to press the wafer against the auxiliarypolishing system.
 16. A polishing system comprising: a wafer supportconfigured to hold a wafer; a first polishing pad configured to polish afirst region of the wafer; an auxiliary polishing system configured topolish a second region of the wafer; a controller communicativelycoupled to the wafer support, wherein the controller is configured tocontrol a position of the wafer support between a first positionbringing the wafer in contact with the first polishing pad and a secondposition bringing the wafer in contact with the auxiliary polishingsystem; and a positioning mechanism connected to the wafer support,wherein the positioning mechanism is configured to rotate the wafersupport about an axis perpendicular to an axis of rotation of the firstpolishing pad.
 17. The polishing system of claim 16, wherein thecontroller is further configured to control supply of a slurry from aslurry delivery system to the first polishing pad.
 18. The polishingsystem of claim 16, further comprising a metrology tool configured tomeasure a thickness profile of the wafer.
 19. The polishing system ofclaim 18, wherein the controller is configured to determine a locationof the second region based on the measured thickness profile of thewafer.
 20. The polishing system of claim 16, wherein the auxiliarypolishing system comprises a plurality of second polishing pads.